Automatic transmissions usually have mechanically driven pumps for hydraulically supplying components e.g. the shifting elements. In this instance, pumps are developed as in-line pumps (coaxial to their drive) or as off-axis pumps, depending on available installation space and design factors; with off-axis pumps, the pump is arranged parallel to the drive shaft of the transmission and is driven by means of a spur gear drive that compensates the axial offset, which in accordance with the state-of-the-art the spur gear drive is normally developed as a straight spur gear stage with a driving and a driven gear.
According to the state-of-the-art, the gear of the spur gear stage, on the side of the starting element or the clutch, fits onto the clutch hub by means of pressfit, where the other gear is arranged on the pump shaft. The deformation of the gear wheel on the clutch side as a result of the pressfit and the long tolerance chain between the clutch gear and the pump wheel across several components and housings has the disadvantage that it results in non-optimal tooth meshing on the spur gear stage and thus in severe gear noise.
In addition, the spur gears can be damaged during the installation of the clutch, since the teeth have to be inserted blind. Another factor is that in the arrangement described, the reactive forces which are created through clutch imbalances and/or distortions, resulting from the long tolerance chain between the gears are transmitted to the inside of the pump, which can result in increased wear of pump bushings and pump wheels.